In most conventional vehicles a vehicle driveshaft or propeller shaft (propshaft) transmits torque from the transmission through a differential to the wheels of the vehicle. The propshaft typically utilizes a pair of splined members that are commonly referred to as a “slip yoke” (outer tube) and a “yoke shaft” (inner tube). The inner tube has a splined outer surface and the outer tube has a splined inner surface. In one example, the inner tube is selectively inserted into the outer tube such that the splines of the outer tube mate with the splines of the inner tube. Such mating may be of an interference or slip fit nature. As a result of this mating, rotational energy from the outer tube may be transmitted to the inner tube or vice versa. The inserted relationship between the tubes also allows for some telescoping movement between the outer tube and the inner tube under certain operational or load conditions.
Various methods are available for forming a spline configuration on the inside surface of the outer tube and the outside surface of the inner tube. One method is to machine the spline configuration into the inner or outer surface of the tubes. Such a method, however, typically requires excess material. Another available method is to use a forming method, such as extrusion, to shape the material of the outer tube or inner tube into its splined configuration. The result of such a forming method is that, for each tube, both the inside and outside surfaces have a splined configuration. Additionally, due to the forming operation, the overall wall thickness for each tube is reduced. Such reduction in thickness causes the mating areas between the inner and outer tube to expand after repeated torsional fatigue loading and to wobble or become out-of-round under load or during operation.